Sunday

March 29, 2015

March 29, 2015

Posted by **mike** on Wednesday, November 30, 2011 at 1:34am.

- arithmetic -
**Reiny**, Wednesday, November 30, 2011 at 8:36amthe third term is 17 ---> a+2d = 17

a = 17-2d

sum of first 8 terms = 220

---> (8/2)(2a + 7d) = 220

4(2a + 7d) = 220

2a + 7d = 55

2(17-2d) + 7d = 55

34 - 4d + 7d = 55

3d = 21

d = 7

then a = 3

sum(6) = 3(6 + 35) = 123

check:

terms are: 3 10 17 24 31 38 45 52 ..

sum(8) = 220

sum(6) = 123

all is good

**Answer this Question**

**Related Questions**

Precalculus - The 8th term in an arithmetic sequence is 5, and the sum of the ...

maths - 1) The first term of arithmetic progression is -20 and the sum of it's ...

math - The sum of the first 10 term of an arithmetic sequence is 145 and the ...

Math - The sum of the first seventeen terms of an arithmetic series is 493 The ...

Arithmetic Progressions - The second term of an arithmetic progression I four ...

Maths - 1..The first 2 terms of a geometric progression are the same as the ...

Math(arithmetic & Geometric Series) - 1)The sum of 6 terms of an arithmetic ...

math - The sum of the first 10 terms of an arithmetic series is 145 and the sum ...

arithmetic - An arithmetic n geometric sequence have the same first term 2.with ...

arithmetic - If the sum is 220 and the first term is 10, find the common ...